<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <title>绘制圆点</title>
  <link rel="icon" href="https://img.kaikeba.com/kkb_portal_icon.ico">
  <style>
    body {
      margin: 0;
      overflow: hidden;
    }

    #canvas {
      background-color: antiquewhite;
    }
  </style>
</head>

<body>
  <canvas id="canvas"></canvas>
  <!-- 顶点着色器 -->
  <script id="vertexShader" type="x-shader/x-vertex">
      attribute vec4 a_Position;
      attribute float a_PointSize;
      void main(){
          //点位
          gl_Position=a_Position;
          //尺寸
          gl_PointSize=a_PointSize;
      }
    </script>
  <!-- 片元着色器 -->
  <script id="fragmentShader" type="x-shader/x-fragment">
      precision mediump float;
      uniform vec4 u_FragColor;
      void main(){
        float dist=distance(gl_PointCoord,vec2(0.5,0.5));
        if(dist<0.5){
          gl_FragColor=u_FragColor;
        }else{
          discard;
        }
      }
    </script>
  <script type="module">
    import { initShaders } from "../jsm/Utils.js";

    const canvas = document.querySelector("#canvas");
    canvas.width = window.innerWidth;
    canvas.height = window.innerHeight;

    // 获取着色器文本
    const vsSource = document.querySelector("#vertexShader").innerText;
    const fsSource = document.querySelector("#fragmentShader").innerText;

    //三维画笔
    const gl = canvas.getContext("webgl");

    //初始化着色器
    initShaders(gl, vsSource, fsSource);

    //设置attribute 变量
    // a_Position=vec4(1,0,0,1)
    const a_Position = gl.getAttribLocation(gl.program, "a_Position");
    const a_PointSize = gl.getAttribLocation(gl.program, "a_PointSize");
    const u_FragColor = gl.getUniformLocation(gl.program, "u_FragColor");

    const a_points = [
      { x: 0, y: 0, size: 10, color: { r: 1, g: 0, b: 0, a: 1 } },
    ];

    //修改attribute 变量
    // gl.vertexAttrib3f(a_Position, 0, 1, 0);
    // gl.vertexAttrib2f(a_Position, 0.5, 0.5);
    // gl.vertexAttrib1f(a_Position, 0.1);

    //声明颜色 rgba
    gl.clearColor(0, 0, 0, 1);
    //刷底色
    gl.clear(gl.COLOR_BUFFER_BIT);

    //绘制顶点
    // gl.drawArrays(gl.POINTS, 0, 1);
    render();

    // 鼠标点击事件
    canvas.addEventListener("click", ({ clientX, clientY }) => {
      console.log(clientX, clientY);
      const { left, top, width, height } = canvas.getBoundingClientRect();
      const [cssX, cssY] = [clientX - left, clientY - top];

      //解决坐标原点位置的差异
      const [halfWidth, halfHeight] = [width / 2, height / 2];
      const [xBaseCenter, yBaseCenter] = [
        cssX - halfWidth,
        cssY - halfHeight,
      ];
      // 解决y 方向的差异
      const yBaseCenterTop = -yBaseCenter;
      //解决坐标基底的差异
      const [x, y] = [xBaseCenter / halfWidth, yBaseCenterTop / halfHeight];

      // gl.vertexAttrib2f(a_Position, x, y);
      // gl.clear(gl.COLOR_BUFFER_BIT);
      // gl.drawArrays(gl.POINTS, 0, 1);
      const size = Math.random() * 50 + 10;
      const n = Math.random();
      const color = { r: n, g: n, b: 1, a: 1 };
      a_points.push({ x, y, size, color });
      render();
    });

    // 渲染方法
    function render() {
      gl.clear(gl.COLOR_BUFFER_BIT);
      a_points.forEach(({ x, y, size, color: { r, g, b, a } }) => {
        gl.vertexAttrib2f(a_Position, x, y);
        gl.vertexAttrib1f(a_PointSize, size);
        // gl.uniform4f(u_FragColor, r, g, b, a);
        const arr = new Float32Array([r, g, b, a]);
        gl.uniform4fv(u_FragColor, arr);
        gl.drawArrays(gl.POINTS, 0, 1);
      });
    }
  </script>
</body>

</html>